Glossary Of Terms

Below are definitions of useful acoustical terms. These definitions are explanatory in nature, rather than technically detailed. Please refer to a qualified professional or text for more precise definitions.

Absorption

When a material reduces the energy of sound reflected off it. By absorbing sound energy, the volume of the reflected sound is reduced.

Acoustic Privacy

When you are able to conduct confidential conversations and are not able to overhear the conversations of others. There are different degrees of acoustic privacy, ranging from none to complete.

Articulation Index (AI)

The measure of the intelligibility of speech. The Index is rated from 0.00 (no intelligibility) to 1.00 (perfect intelligibility). The range is divided into four qualitative privacy categories, including Confidential (0.00 to 0.05), Normal (0.05 to 0.20), Marginal (0.20 to 0.30), and None (0.30 to 1.00).

A-Weighted Sound Level (dBA)

The standard measure of the sound pressure level that approximates the sensitivity of the human ear at moderate sound levels. A-Weighted Sound Level de-emphasizes high and low frequencies because the ear poorly perceives these.

Background Noise

Background noise is the noise present in an environment, other than the desired or foreground sound. Also referred to as ambient noise, it is the combination of all sounds generated both near and far.

Centralized Sound Masking System

Centralized systems consist of a centrally-located rack of electronic equipment used for masking generation, volume and equalization adjustments, and amplification. This equipment is connected to a set of loudspeakers installed above the ceiling that reproduce the centrally-generated masking sound.

Decentralized Sound Masking System

Decentralized systems consist of Master and Satellite Units. The Master includes the electronics for sound generation, and controls for volume and contour adjustment. Local changes must be made by entering the ceiling and physically accessing those controls. Only global volume changes and timer functions can be centrally controlled. Also referred to as distributed or self-contained systems.

Decibel(dB)

The unit of measure for sound pressure level (volume).

Dynamic Range

The variation in sound levels over time, or the difference between the loudest and quietest sounds measured over a period of time.

Equalizer

An audio system component that allows for the adjustment of the volume of specific frequency bands. Typical equalizers allow adjustment for each octave or one-third octave.

Equivalent A-Weighted Sound Level (Leq)

The equivalent constant sound level for a varying sound level measured over a period of time. Also referred to as the Equivalent Average Sound Level.

Frequency

The number of cycles of sound waves per second.

Hertz(Hz)

The unit of measure for frequency.

Intelligibility

The degree to which a conversation can be understood or is comprehensible.

Loudness

A person’s subjective perception of the volume of sound. A 10dB increase in sound energy is generally perceived as a doubling in loudness.

Masking

The effect of reducing or eliminating the ability to hear a sound due to the presence of a masking sound.

Networked Sound Masking System

The LogiSon Sound Masking System provides a complete system – random masking sound generator, amplifier, and separate volume and equalizer controls for masking and paging – in each Primary Hub. A small wall-mounted control panel provides central control of each of these features, as well as paging and timer functions. The hubs and speakers are typically installed above the ceiling.

Noise

Any unwanted sound. Note that not all sound is considered noise.

Noise Floor

The lowest sound pressure levels present in a space over a period of time.

Noise Reduction Coefficient(NRC)

The measure of acoustical absorption calculated at specific mid-range frequencies. The Noise Reduction Coefficient is commonly used to rate the performance of acoustical ceilings.

Octave Band

Bands of frequency into which audible sound is divided for frequency analysis. One-third octave bands further divide each octave into three segments.

Phasing or Phasing Effect

Occurs when identical sound waves from two speakers meet in the area between the two speakers. Constructive or destructive interference occurs, causing uncontrollable variations in the sound volume and frequencies.

Pink Noise

A broad-spectrum sound exhibiting equal sound energy per octave. Each octave contains double the frequency range of the one before. In order to maintain equal energy, the volume must reduce at 3dB per octave.

Quiet

The absence of noise. Quiet can be distinctly different from “silence.” Silence is the absence of all sound, while quiet is the absence of noise (i.e. unwanted sound).

Random Noise

A sound signal with no repetitive pattern.

Reverberation

The persistence of a sound in a space due to many reflections of that sound from the surfaces in the space after the sound source has been stopped. Reverberation can be compared to a multitude of indistinguishable echoes.

Room Criteria

A quantitative and qualitative assessment of noise. The numeric component is the average of the sound pressure levels at the 500, 1000 and 2000 Hz octave bands, while the qualitative component classifies the noise as containing Rumble (R), Hiss (H), Vibration (V), or as being Neutral (N). The Room Criteria curves approximate the balanced spectrum found acceptable by most people.

Silence

The absence of any sounds. Silence differs from “quiet,” which is the absence of unwanted sounds. A space can be considered quiet even if an unobtrusive background sound is present.

Sound Level

The measure of the sound pressure level using weightings that emphasize certain frequencies. Weightings include designations such as A, B and C.

Sound Level Meter

A device used to measure sound pressure levels. Meters consist of a microphone, amplifier, output meter, and frequency-weighting protocols.

Sound Masking

See the definition for Masking.

Sound Pressure Level (SPL)

The measure of the amplitude or volume of sound. Sound Pressure Level is measured in decibels (dB).

Sound Transmission Class (STC)

A classification of the sound-insulating properties of a material or structure. Sound Transmission Class is commonly used to rate office walls and furniture partitions.

Spectrum

The composition of a sound expressed in frequency and amplitude.

Transmission Loss (TL)

The measure of the sound-insulating properties of a material or structure, expressed as the number of decibels by which a sound is reduced in passing from one barrier (e.g. a wall or furniture) to another.

White Noise

A broad-spectrum sound exhibiting equal sound energy across the entire frequency range. Volume stays constant as the frequency increases; however, subjectively it appears that higher frequencies are louder, giving it a hissing quality.